1. Field of the Invention
This invention relates to a rotor iron core of a permanent magnet type generator more particularly, the invention relates to a rotor with permanent magnets in which a plurality of permanent magnets are fixed on the outer circumference of the rotor iron core. A method of manufacturing such a rotor is also part of the invention.
2. Description of the Related Art
Hitherto, the rotors of a permanent magnet type generator, in which permanent magnets are disposed on the outer circumference, have required various methods to facilitate positioning, holding and fixing the permanent magnets. One fixing method is to bond the permanent magnets on the outer circumference of the rotor by winding over the outer circumference a glass tape or the like, impregnated with a semi-hardening resin. The glass tape has the same width as the width of the permanent magnet, and is wound several times in an overlapping manner. Another fixing method is to wind the outer circumference with a tape, such as a clothing tape, having a width narrower than the width of the permanent magnet. The tape may be wrapped with a half-wrap winding to fix the permanent magnets Similar methods have been carried out. Another method of disposing the permanent magnets is to mold the entirety in synthetic resin. This method has also been carried out.
However, in the field of electric rotating machines, rotating machines (such as electric motors and the like) are operated at a high speed in recent years. Accordingly, the centifugal force of the rotor becomes large. As a result, strength has become problem with respect to holding and fixing of the permanent magnet.
For example, in the Japanese Utility Model Application Laid-open No. 57055/1994 publication, there has been proposed a method in which iron plates of the same shape provided with projections at fixed intervals on the outer circumferential surface of the stacked iron core are stacked in the state where corresponding projections of respective iron plates are caused to be respectively in correspondence with each other to form projected stripe portions on the outer circumferential surface to dispose permanent magnets in circular arc form in the state where both side end surfaces are caused to be in parallel to each other between those projected stripe portions to weld the projected stripe portions and the permanent magnet surfaces to fix the permanent magnets on the outer circumference of the rotor iron plates. However, this method requires a complicated step to allow the both side end surfaces of the permanent magnets to be in contact with the projected stripe portions to dispose the permanent magnets between the respective projected stripe portions to fix them by welding, etc. Moreover, in the Japanese Utility Model Application Laid-open No. 21346/1944 publication, there has been proposed a method in which magnets are fitted between projections of fixed intervals formed on the core outer circumference of the rotor iron core to fix a cylindrical cover of resin over the outer circumferential surface thereof so that the entirety is covered.
For example, in the Japanese Patent Application Laid open No. 46757/1985 publication, there has been proposed a rotor in which the field magnetic core and the magnets forming the rotor are bonded and fixed by bond, etc. to wind the outer circumferential side with a bind tape to thermally harden the resin component of the bind tape to cut and grind the bind tape surface to coat varnish on the surface thereof to smooth it. However, it was necessary to carry out a step of forming the outer circumference of each end ring of the both end plates so that it is higher than the finishing surface at the beginning to grind or polish the surface thereof after undergone heating and fusing to implement cutting thereto to smooth it.
Moreover, in the Japanese Utility Model Application Laid-open No. 43751/1993 publication, there has been proposed a fixing method in which rotor plates are stacked to form a field iron core to dispose magnets on the outer circumferential surface side thereafter to dispose end plates on the both ends of the field iron core to fix, by plural caulking pins, the stacked field iron core by the end plates in order to allow it to be firmly put therebetween to wind a metallic bind wire on the outer circumferential surface thereof to clamp the terminating end of the bind wire by the caulking pins of the both side end plates.
In accordance with this method, it was necessary to wind the bind wire thereafter to adjust clamping degree of the field iron core by loosening caulking pins to secure, by winding, the front end of the bind wire to tighten the caulking pins for a second time.
Further, the invention described in the Japanese Patent Publication No. 87636/1994 is directed to a method of manufacturing a rotor with permanent magnet, in which bow-shaped permanent magnets are disposed on the outer circumferential surface of the field iron core to provide resin injection holes at both side end plates to form grooves at the boundary portion between the permanent magnets to wind adhesive tape so as to cover these grooves to cover the boundary grooves thereafter to wind a semi-hardening resin impregnated tape on the outside thereof, and to fill resin into the grooves through the resin injection holes of the end plates to heat the entirety thereof to fuse the resin thereafter to solidify it.
In addition, as for the performance, gap between the rotor and the stator is important. Particularly, the positional shift of the magnet in the rotational axis direction is the great problem that it affects power generating efficiency.
For example, a method described in the Japanese Utility Model Application Laid-open No. 172268/1987 publication is a method in which, in fixing permanent magnets on the rotor body, positioning ring is disposed at the outside of the shaft to hold and fix the permanent magnets on the rotors by the positioning ring to wind a reinforced wire on the outside thereof to further cover the outside thereof by resin, thus to fix the permanent magnets.
In the case of a conventional method of fixing permanent magnets on the outer circumference of the rotor iron core as described above, a plurality of projections are provided on the outer circumference of the rotor iron core to dispose permanent magnets between respective projections to weld projected stripes and the permanent magnets, to wind insulating tape such as glass tape, etc. on the outer circumferential surfaces of the permanent magnets, or to carryout resin molding to cover the outside thereof with resin thus to manufacture the rotor. However, since the permanent magnet is generally comprised of fragile ferrite, etc., when the permanent magnet is forced into the portion between projections on the outer circumferential surface of the rotor iron core, the corner portion of the permanent magnet may be broken because the projection is firm. If the permanent magnet is forcedly thrust thereinto, the permanent magnet may be broken during working. Accordingly, it was necessary to manufacture rotor in the state caused to have clearance between the permanent magnet and the projection in order that the permanent magnet is not caused to come into contact with the projection. For this reason, a method of winding a broad resin impregnated tape, etc. on the outer circumferential surface is carried out in order to prevent the permanent magnet from protruding by the centrifugal force of the permanent magnet. However, in such taping work, there may take place positional shift of the permanent magnet. As a result, it was difficult to manufacture rotor iron core stably rotating. Moreover, the manufacturing process was also complicated in order to guarantee that no positional shift takes place. In addition, a method of disposing permanent magnets thereafter to fit and cover a cylinder over the outer circumferential surface of the entirety of the rotor iron core is also carried out. In this case, however, a cylindrical cover or the like is required, resulting in high cost. The rotor cannot be manufactured at a low cost.
With these conventional fixing methods, there are problems as described below from a viewpoint of preference. Namely, projections of metal system are disposed between permanent magnets disposed on the outer circumference and the entirety is heated. Accordingly, there takes place beads, etc. formed on the surface by fusion owing to heating. For this reason, any gap is required between the stator and the rotor, resulting in magnetic leakage. This was not preferable from a viewpoint of the magnetic efficiency of the generator.
In addition, the conventional rotor iron core is fragile with respect to contact and/or impact. Accordingly, it was the great task to allow permanent magnets to undergo positioning on the field iron core to fix them thereonto in the state where they are not damaged.